AMERICAN GEOLOGY DECADE OF 1840-184!). 399 



the Boston Society of Natural History in April, 1846, Binney exhibited 

 a collection of fossil shells from the so-called Bluff formation at 

 Natchez, on the Mississippi, and announced the belief that the forma- 

 tion was analogous to the Loess of the Rhine Valley and a result of 

 fluviatile action rather than attributable to the glacial drift. 



In 1847 J. D. Dana, who from the beginning of his career had shown 

 a disposition and ability to grasp the broader, more profound ques- 

 tions of geology, came forward with two papers which were beyond 

 question the most important of the year. The first of 



Dana on the . , , , 



Geological Results of these had to deal with the g'eolooical results of the 



the Earth's . . , .. 



Contraction and the earth s contraction in consequence of cooling and 



Grand Outline 1 . t . . •,. 



Features of the involved the acceptation on his part of the prevailing 



theory that the earth was once in a condition of igne- 

 ous fluidity. After a full discussion of the subject and the views held 

 by others, Dana announced it as his belief that the now oceanic areas 

 were atone time the most intensely heated portions of the crust, and 

 had, therefore, on cooling undergone the greatest amount of contrac- 

 tion, and that, further, the mountain ranges and main fissures along 

 the oceanic borders are due to this same contraction. Such a theory, 

 he felt, did away with the almost preposterous though prevalent idea 

 that continents and mountains have been lifted up by a force acting 

 from beneath, a force which could not be satisfactorily located and 

 accounted for; a theory which would not account for the mountains 

 retaining their positions, even did it offer satisfactory explanation for 

 their first production. 



He showed, further, that the folding and faulting of the strata as 

 described by the Rogers brothers in Virginia and Pennsylvania could 

 be readily accounted for on the theory of a force acting laterally, and 

 that such folds w T ould have their steepest incline on the side farthest 

 from the source of movement and would also be most abrupt nearest 

 this source. The fact that such results were not in all cases uniform, 

 he conceived as being due to variation in the thickness of the beds, to 

 a want of uniformity in the materials, and inequality in the action of 

 the force upon the different parts of the line along which it operated. 



The geological epochs were regarded, as announced in this same 

 paper, as perhaps due to the alternation of prolonged periods of quiet 

 with those of more or less abrupt change, due to contraction. The 

 idea that mountains might be produced by tides and paroxysmal move- 

 ments beneath the crust (as advocated by H. D. Rogers) was set aside 

 on the ground that such should have occurred at earlier periods, and, 

 further, it would not account for the principal ranges in the east and 

 west of the continent. In many of the views he here advanced Dana 

 agreed with those previously advanced by the French geologist Prevost. 



In the second paper referred to, on the Grand Outline Features of 

 the Earth, Dana argued "that the great chain of mountains, as well as 



